In many situations, there is a need to bond separated tissues or to seal defects in tissues. Sutures and staples are effective and well established wound and tissue defect closure devices. However, there are surgical techniques where classical repair procedures are unsatisfactory, limited to highly trained specialists (e.g., microsurgery), or not applicable due to tissue or organ fragility, inaccessibility (e.g., endoscopy procedures), or loss of gases or fluids, including capillary "weeping". Tissue adhesives and sealants have been developed to meet these needs. They may be used to seal or reinforce wounds that have been sutured or stapled, as well as finding independent use. The leading commercial products are fibrin glues and cyanoacrylates. However, both products have significant limitations which have prevented their widespread use.
In this regard, one of the major limitations encountered in the development and/or use of tissue adhesive and sealant compositions is their inability to form a sufficiently strong bond to tissues. Therefore, tissue adhesives and sealants may have to be employed in combination with sutures and/or staples so as to reduce the tissue bonding strength required for acceptable performance. As described above, however, there are many indications where the use of sutures and/or staples is undesirable, inappropriate or impossible.
As demonstrated by the Applicants herein, mechanical failure of bonds formed by tissue adhesive and sealant systems may occur at the interface between the crosslinked adhesive matrix and the tissue. The inability of the adhesive matrix to form a strong interface or bond with tissues is most likely due to the fact that native collagen present in the tissue is a highly aggregated, insoluble protein which, because of its physical characteristics, is not readily amenable to non-covalent and/or covalent interactions with the tissue adhesive or sealant components as applied and/or during and after curing. As a result, for most tissue adhesive and sealant systems, failures are generally believed to occur at the interface between the crosslinked adhesive matrix and the tissue collagen itself.
One possibility for improving the mechanical performance of a tissue adhesive or sealant is to strengthen the interface between the collagen protein of the tissue and the adhesive matrix by altering the physical characteristics of the adhesive or sealant components to more closely approximate those of native collagen, thereby making the two components more compatible and amenable to non-covalent and/or covalent interaction. As one example, bonding of a dental restoration to the dentine of a tooth requires the establishment of adhesion between the demineralized collagen present in the dentine and a methacrylate adhesive matrix. In one study, alteration of the vinyl monomers present in a methacrylate adhesive matrix to more closely match the solubility parameter of collagen present in the dentine resulted in an increased strength of bonding of a dental restoration. (Miller, Adhesive Bonding to Dentin with Isocyanate Copolymers", Ph.D. Dissertation, University of Missouri--Columbia (1995)). However, the development of physiologically acceptable adhesives and sealants which closely match the characteristics of native collagen has, for the most part, been unsuccessful. Moreover, methods for altering collagen present in a tissue to be more compatible for covalent and/or non-covalent interaction with adhesive or sealant components have heretofore not been described.
There is, therefore, a need for novel methods for enhancing the adhesion of adhesive or sealant compositions to tissues. More specifically, there is a need for novel methods of strengthening the adhesive matrix/collagen interface so as to enhance the mechanical properties of bonds created by tissue adhesives and sealants, wherein those methods are generally applicable to a variety of different tissue adhesive and sealant systems.